Thanks to all who replied. Have purchase a LaCie d2 Quadra 3 TB external hard drive. Connected it to my machine via e-sata. It shows that it is only 746 GB.
My other drives are western digital and are 1 TB and 2TB, these show their proper
capacity, whereas my Lacie 3 TB does not.
While I am waiting for LaCie to respond, anyone have any ideas?